The present invention is directed to bicycles and, more particularly, to an apparatus for controlling a voltage generated by a bicycle dynamo.
Automatic transmission shifting devices are commonly provided in newer bicycles. Such bicycles often employ an electrically powered transmission. Accordingly, a dynamo is usually provided for generating electrical power, and a charging system is provided for charging a battery or other voltage storing device used to supply the electrical power to the electrically powered transmission. The dynamo in such a system typically generates voltage in a manner proportional to the rotational speed of the bicycle wheel. In some instances, the generated voltage may exceed 100 V at high speed. It is thus necessary to design the elements of the charging system and any other elements that are driven by the voltage generated by the dynamo to withstand high voltage. However, elements capable of withstanding high voltage lack versatility and are expensive.
As shown in FIG. 1, the voltage generated by a dynamo typically increases with the resistance of the dynamo load and with an increase in wheel speed. Thus, a high resistance load could be damaged during high speed riding conditions unless the load is constructed to withstand such high voltages. Also, as shown in FIG. 2, a high resistance load increases the torque required to rotate the dynamo at higher speeds, whereas a low resistance load decreases the torque required to rotate the dynamo at higher speeds. The cause of this tendency lies principally with overcurrent loss generated within the dynamo. Thus, not only must high resistance loads be constructed to withstand high voltages, but the rider must exert greater pedaling forces to rotate the dynamo at higher speeds.
The present invention is directed to various features of a device for controlling the application of power from a dynamo to a load. In one embodiment, a device is provided for preventing high voltage from acting on a load driven by a bicycle dynamo. The device comprises a sensor circuit and a control circuit. The sensor circuit senses an operating signal derived from the dynamo, wherein the operating signal corresponds to a voltage generated by the dynamo. The sensor circuit also provides a control signal when the operating signal passes a threshold value. The control circuit is operatively coupled to the sensor circuit and is adapted to be coupled between the dynamo and the load to control the current delivered to the load in response to the control signal.
Additional inventive features will become apparent from the description below, and such features alone or in combination with the above features may form the basis of further inventions as recited in the claims and their equivalents.